Fig 1-5: rib arrangement Fig 1-6: rib design 1. 2.4 Support Surface When plastic parts need to have a support surface, it is not desirable to use the whole part bottom surface as the support. Fig 1-7 shows the bottom surface becomes uneven, when the plastic part deforms a bit. A Frame, three or four bottom feet are usually a better support surface Fig. 1-7: design of support surface 1. 2.5 Draft Draft is used to protect plastic part surface from scratch during ejection. It is a draft reserved along with the ejection direction. The draft depends on the material shrinkage, part shape, wall thickness, and ejection location For inner holes on a plastic part, the smaller end of core is used as reference. Its draft is shown along with the rising direction. For exterior of a plastic part design, the larger end of cavity is used as reference. Draft is dimensioned along with the reducing direction Please refer to Table 1-3 for various draft designs. A typical draft ranges between 30-1 30. Normally a tall or large plastic part design has a smaller draft. When there is a special need or higher precision requirement, a smaller daft is usedFig.1-5: rib arrangement Fig.1-6: rib design 1.2.4 Support Surface When plastic parts need to have a support surface, it is not desirable to use the whole part bottom surface as the support. Fig.1-7 shows the bottom surface becomes uneven, when the plastic part deforms a bit. A Frame, three or four bottom feet are usually a better support surface. Fig.1-7: design of support surface 1.2.5 Draft Draft is used to protect plastic part surface from scratch during ejection. It is a draft reserved along with the ejection direction. The draft depends on the material shrinkage, part shape, wall thickness, and ejection location. For inner holes on a plastic part, the smaller end of core is used as reference. Its draft is shown along with the rising direction. For exterior of a plastic part design, the larger end of cavity is used as reference. Draft is dimensioned along with the reducing direction. Please refer to Table 1-3 for various draft designs. A typical draft ranges between ' ' 30 1 30 ° − . Normally a tall or large plastic part design has a smaller draft. When there is a special need or higher precision requirement, a smaller daft is used